The TRAPPIST-1 system provides an extraordinary opportunity to study multiple terrestrial extrasolar planets and their atmospheres. Here we use the National Center for Atmospheric Research Community Atmosphere Model version 4 to study the possible climate and habitability of the planets in the TRAPPIST-1 system. We assume ocean-covered worlds, with atmospheres comprised of N2, CO2, and H2O, and with orbital and geophysical properties defined from observation. Model results indicate that the inner three planets (b, c, and d) presently reside interior to the inner edge of the traditional liquid water habitable zone. Thus if water ever existed on the inner planets, they would have undergone a runaway greenhouse and lost their water to space, leaving them dry today. Conversely the outer 3 planets (f, g, and h) fall beyond the maximum CO2 greenhouse outer edge of the habitable zone. Model results indicate that the outer planets cannot be warmed despite as much as 30 bar CO2 atmospheres, instead entering a snowball state. The middle planet (e) represents the best chance for a presently habitable ocean-covered world in the TRAPPIST-1 system. Planet e can maintain at least some habitable surface area with 0 - 2 bar CO2, depending on the background N2 content. Near present day Earth surface temperatures can be maintained for an ocean-covered planet e with either 1 bar N2 and 0.4 bar CO2, or a 1.3 bar pure CO2 atmosphere.

5. Concluding remarksIn this study, we calculated the boundaries of the so called Habeer-table Zone. We showed that planetary ha-beer-tability iscritically dependent on the carbonation level of a potential beer ocean, as well as its degree of alcohol. From this definition, we derived a new combination of biomarkers that should be used in the future - in particular with JWST through transit spectroscopy - to detect and characterize beer planets.We know that Earth-like planets, Jupiler-like planets... are common in our galaxy and by extension in the Universe. Following the discoveries of the TRAPPIST-1 planets, and given the large extent of the Ha-beer-table zone as calculated in our study, beer planets should also be extremely common in our galactic neighborhood.More generally, our work raises the question of how extraterrestrial life would evolve on beer planets. At first sight, beer should be a solvent at least as good as water for life to emerge (Miller 1953). However, we are worried about what form would take natural selection on such planets and if drunk living organisms would really be able to evolve in what we - humans - call the intelligent life paradigm. If beer planets are really common, this is an alternative scenario that should be assessed to solve theFermi paradox.

Also interesting to note the conclusions about the state of the ice envelope inferred on TRAPPIST-1f: apparently it is unlikely to be an ocean world.

Using the H2O-REOS equation of state for water (French et al. 2009; Nettelmann et al. 2010) and thermal evolution models of Lopez & Fortney (2014), we find that even at an age of 8 Gyr the temperature at the bottom of such an envelope will be ≳1400K and the pressure will reach ≈130 kbar. For comparison, the pressure in the deepest parts of Earthís oceans is ≈1 kbar. Moreover, these calculations donít include the possibility of significant tidal heating from planet-planet interactions, which could raise the interior temperature even higher. At such a high pressure and temperature, water will be far beyond the triple point and far too hot for high pressure ices like ice VII and X. Instead, it will exist as a high pressure molecular fluid, much like the deep interiors of Neptune and Uranus (Fortney et al. 2011; Nettelmann et al. 2011). Therefore, liquid water will likely only exist in clouds near the top of TRAPPIST-1fís atmosphere and our results suggest that it is no more likely to be habitable than any other gas or ice-giant with water clouds in its atmosphere.

Lazarus wrote:Also interesting to note the conclusions about the state of the ice envelope inferred on TRAPPIST-1f: apparently it is unlikely to be an ocean world.

Using the H2O-REOS equation of state for water (French et al. 2009; Nettelmann et al. 2010) and thermal evolution models of Lopez & Fortney (2014), we find that even at an age of 8 Gyr the temperature at the bottom of such an envelope will be ≳1400K and the pressure will reach ≈130 kbar. For comparison, the pressure in the deepest parts of Earthís oceans is ≈1 kbar. Moreover, these calculations donít include the possibility of significant tidal heating from planet-planet interactions, which could raise the interior temperature even higher. At such a high pressure and temperature, water will be far beyond the triple point and far too hot for high pressure ices like ice VII and X. Instead, it will exist as a high pressure molecular fluid, much like the deep interiors of Neptune and Uranus (Fortney et al. 2011; Nettelmann et al. 2011). Therefore, liquid water will likely only exist in clouds near the top of TRAPPIST-1fís atmosphere and our results suggest that it is no more likely to be habitable than any other gas or ice-giant with water clouds in its atmosphere.

Bad news for the habitability of planet F...Is there any good news for D, E or G?

Still not enough to rule out the life possibility in one of planets in the habitable zone

First TRAPPIST-1f e g for example like other planets of this system it's very likely to getting energy also by gravitational tidal heating plus the star energy to keep an ocean liquid

Second Frequent flaring it's likely to not be a barrier for a ocean world even if one of this planets has continents life from this ocean it's likely to adapt the surface by the evolution as we know it.

third it's seems that planets around flare stars can keep the atmosphere see the GJ1132b case.

So in the end of the day it's too early to jump for conclusions and rule out this planets and others similar system in the Galaxy of the potential planets with life.

Last edited by Daniel on 13th April 2017, 4:09 am; edited 2 times in total

If GJ 1132 b has atmosphere being closer to its host which is much larger and hotter than Trappist 1 so all planets around this very small star which are potentially habitable d ,e ,f, g surely have atmospheres.We do not know exact mass of planet f to judge habitability now and I wonder why error bars for mass of this planet is so small comparing to other planets in this system

New mass measurement are kind of joke how it is possible these planets have so low densities similar to Neptune? It would requires 70% of water content for e,f,g planets. Large discrepancy between b and c planets is weird but between c and g with similar radius is even weirder.I do not buy it

This is a new regime not experienced in solar system planets: there is no magnetopause at which the planetary field pressure balances the wind pressure. Instead, stellar wind particles can constantly precipitate directly down open field onto the atmosphere. The concept of atmospheric protection by a planetary magnetic field does not hold here and is likely not to hold in the conventional sense for the TRAPPIST-1 planets. The TRAPPIST-1 system represents a new challenge to atmospheric evolution and survival on close-in planets around very low mass stars.

Interesting to consider how a mini-Neptune would survive under these conditions.

Hubble delivers first hints of possible water content of TRAPPIST-1 planets

An international team of astronomers used the NASA/ESA Hubble Space Telescope to estimate whether there might be water on the seven earth-sized planets orbiting the nearby dwarf star TRAPPIST-1. The results suggest that the outer planets of the system might still harbour substantial amounts of water. This includes the three planets within the habitable zone of the star, lending further weight to the possibility that they may indeed be habitable

That's fantastic news. They may not be bone-dry irradiated, atmosphere-less rocks.Edit: It doesn't look like this is being reported very clearly. HST did not detect anything related to water content in the planets. It just refined the star's luminosity and set evolutionary constraints on the water content of the planets.